The present invention relates to waste water treatment method and apparatus and more particularly, the present invention relates to separating contaminants from an aqueous solution using mass transfer techniques and electrocoagulation.
The problem of separating or removing contaminants from aqueous systems has been a complication that the art has lamented over for many decades. To this end, the art developed along with further industrial processes as water contamination grew commensurately with industrial progress. Initially, water treatment was simply a matter of adding materials suitable for inducing precipitation of certain materials, filtration, ion exchange and other processes. With the continual increase in strict requirements for clean water, electro chemistry was brought into favor. Broadly, the use of electrodes disposed within a cell and subjected to electric current was found to be useful for treating solutions containing contaminants. In some instances, other unit operations were combined with this treatment process in order to render inert compounds.
One of the references that was selected for review is U.S. Pat. No. 1,095,893, issued to Landreth, May 5, 1914. This patent relates to electrochemical treatment and in this patent, the patentee has identified that such cells are useful for the treatment of water. As stated in the disclosure electrodes of copper, aluminum, brass or other alloys are useful as cell plate material. In addition, the disclosure discusses the fact that settling tanks may be useful to assist in material settling (floccing). Column 2 of the disclosure indicates that the series of electrodes are arranged so that the water passes up through the apparatus and is forced to xe2x80x9c. . . to take a circuitous course whereby any material added to it or found in it may be thoroughly mixed and all particles of the liquid be brought into contact with the electrodes . . . xe2x80x9d. It is also as stated in the text at column 2, that the electrodes are in the form of horizontally disposed plates and that the plates may be provided with apertures which may be centrally arranged with the plates of alternating series of other plates have recesses at their ends. Column 3 of the disclosure states:
xe2x80x9cTo provide for the proper passage or circulation of the liquid between plates 14 and its movement throughout the apparatus, alternate plates are provided with apertures indicated at 14A, while the intermediate plates have their cut-away comers notched or recessed as at 14B as clearly illustrated in FIGS. 8 and 9. By this means, the liquid under treatment is diverted in its flow and caused to contact with the entire surface of the respective plates, insuring the desired electrical treatmentxe2x80x9d
Although this disclosure is useful for instructing the procedure for electrochemical treatment of water, there is no indication of the addition of an oxidant material such as ozone. Further, the teachings of this patent are limited to electrochemistry; the disclosure fails to set forth any details with respect to dissolved air flotation, fluid hydrodynamics, cavitation, flocculation or any other fluid dynamic principles that would augment the utility of the electrochemical cell taught in this patent.
In U.S. Pat. No. 1,146,942, issued to Landreth, Jul. 20, 1915, a variation on what has been discussed in the previous patent is set forth. In this reference, there is a clear indication that the electrodes are of a different polarity and that a suitable pole changing switch, an example is given as number 26 in the drawings, could be used to switch the current in order that one set of plates act as cathodes for a certain length of time while another set of plates act as anodes during this period of time. This reference advanced the art by providing a reverse polarity arrangement for changing the polarity of the individual cells within the unit. The reference, similar to its companion, is deficient on appreciation of countercurrent oxidation with a dissolved gas. Further, it is believed that this apparatus would not be particularly well suited to handling a wide variety of contaminant types (organic, inorganic, combinations thereof, etc.)
In a further reference issued to Landreth, namely U.S. Pat. No. 1,131,067, issued Mar. 9, 1915, there is a discussion of reintroducing treated liquid for further treatment by the apparatus as well as a discussion concerning oxidizing treatment or a treatment for the production of flocculent formed either from the metal electrodes or from simple chemical reaction or the latter stimulated by electric current; or any other treatment. At column 2, beginning at line 25 et seq., discusses recirculation of the material for further treatment in the apparatus.
Preis et al., in U.S. Pat. No. 3,728,245, issued Apr. 17, 1973, teach an apparatus for treating sewage incorporating a series of electrolytic plates for the purpose of electrocoagulation. The patentees discuss a need for maintaining pressure in the circuit so that chlorine and ozone are maintained in solution in order to enhance bactericidal action. This reference advanced the art developed by Landreth et al., by employing an oxidant to enhance the electrocoagulation. The reference, although providing further instruction in this art, is deficient any discussion cavitation or floc generation by pressure discontinuities in an outlet stream of treated aqueous material.
Other generally relevant references include U.S. Pat. No. 913,827, issued to Korten, Mar. 2, 1909, U.S. Pat. No. 3,523,891, issued to Mehl, Aug. 11, 1970, U.S. Pat. Nos. 5,928,493; 5,705,050; 5,746,904 and 5,549,812, 3,846,300, 5,587,057 and 5,611,907.
The electrolytic processes were found to be generally useful, however, the cellular design was such that the electrodes often would accrue debris and, therefore, would change the requirements of the current of the cell. In addition, many of the plates in the existing arrangements were fairly large and did not provide any improvement to enhance the surface area to therefore increase the number of reactions with the contaminants to be treated in the water. This, of course, leads to lower degree of interactions and a higher cost of running the cell in terms of the current requirements due to debris buildup.
It has also been proposed to employ dissolved air flotation systems. One such arrangement is made by the Precision Environmental Systems Company. This company manufactures devices which are useful for flocculation and coagulation within the same unit. This unit is quite useful for the purpose for which it was designed, however, the arrangement has an extremely large footprint and does not provide for different chemical processes to occur within the same unit.
Of the more desirable arrangements that have evolved in this art for water treatment are perhaps the use of dissolved gases for the purpose of oxidation has been moderately successful. In the art that is currently known, typically oxidation cells are open to atmospheric pressure where a gas dissolved in solution is allowed to evolve out of the solution. The arrangement in the art provide a tortuous path or other applied force in order to keep the bubbles in solution as long as possible. This has the advantage of providing a reaction site (the surface of the bubble) of the oxidant material so that the contaminant can be oxidized. Once the gaseous material then evolves to the surface, the contaminant is flocculated and the materials then separated. This is broadly known as aeration and various devices have been proposed in this art in order to maintain the bubbles in solution and thus enhancing the degree of interaction of the bubble surface with the material to be oxidized or otherwise decontaminated.
It would be desirable if there were a process whereby a gaseous oxidant could be introduced into a reservoir or other chamber or confined area under sufficient pressure to maintain the gas in solution. This affords the opportunity for the smallest possible bubbles in solution to oxidize contaminants present in the solution. It would be particularly desirable if there were a system available where the dissolved oxidant gas could be maintained in solution in order to provide the smallest possible bubbles and therefore the greatest possible degree of surface area for reaction with the contaminants to be separated and further, affording control of the bubble size.
The present invention is directed to providing a mass transfer mechanism and advanced oxidation technologies for the separation of contaminants from an aqueous solution where the oxidant is maintained in solution until such time as it is desirable to allow the pressure to be reduced and the oxidant to come out of solution.
One object of one embodiment of the present invention is to provide an improved method of separating contaminants from aqueous solution. A countercurrent mass transfer mechanism is employed.
A further object of one embodiment of the present invention is to provide an electrocell for use in electrochemical separating contaminants from an aqueous solution, the reactor having a divergent inlet stage and an inlet suitable for receiving the aqueous solution containing contaminants and an outlet for discharging effluent, the inlet stage diverging in cross-sectional area from the inlet to the outlet; electrodes in electrical communication with the inlet stage in spaced relation and connectable to a source of power for supplying current to the electrodes; a plurality of discrete fluidizable metal reaction surfaces freely fluidizable within the inlet stage for electrochemically oxidizing the contaminants in the aqueous solution in the presence of the electrodes to isolate the contaminants.
With respect to the oxidant, ozone is one of the preferred oxidants for use in the present invention, however, it will be readily appreciated that any other suitable oxidant could be used such as chlorine, bromine, hydrogen peroxide, suitable nitro compounds, inter alia.
It has been found that by effectively providing an inverted or reversed aeration system that effective oxidation of the contaminant can be achieved. The reservoir may be an isolated chamber, tube with closed ends or, alternatively, may comprise an earth formation for subterranean treatment of contaminants in an aqueous solution. In the instant methodology, the inlet is disposed at a higher elevation than the outlet. In this manner, the incoming entrained gaseous oxidant is forced downwardly through the solution and, therefore, will act in a countercurrent manner with the aqueous solution to be treated. By maintaining a super atmospheric pressure in the chamber reservoir container, etc., the gaseous oxidant is maintained in solution and in very fine bubbles. This has produced marked results, since the smaller bubbles provide a significantly improved surface area for contact with the contaminants to oxidize the latter. This is achieved by control of the pressure into the reservoir and the pressure at the outlet thereof. In this manner, the pressure is effectively adjustable and can be customized by the user. This is in marked contrast to the prior art which effectively provide open vessels and, therefore, allowed the pressure to equalize at atmospheric pressure and simply provided convoluted or otherwise tortuous paths through which a gas was forced. The concept in the prior art was to provide the tortuous path in order to try and keep the bubbles in solution and, therefore, at least partially in contact with the material to be treated. The technique of the prior art is effectively an aeration technique where a gas is forced through a solution for oxidation purposes.
The difference in the instant application is quite pronounced and results in a significant advance in this art. It has been found that by maintaining the pressure within a confined chamber, the gaseous oxidant can be maintained in solution for a user selected duration; this is in contrast to what the prior art proposes. The instant case permits control of the bubble size of the oxidant within the chamber and facilitates countercurrent contact with the oxidant bubbles and aqueous solution and further allows for user selected pressure discontinuity in the form of, for example, hydraulic cavitation, to induce floc formation. Control on this level has not been previously proposed in the prior art whatsoever; the prior art effectively used a xe2x80x9chit and missxe2x80x9d process of aeration as opposed to a controlled process, which also results in the formation of a rich floc and clean aqueous solution.
As a generic overview of the present invention, the same unifies a series of technologies including dissolved air flotation, hydraulic cavitation, fluid dynamics, mass transfer and electrocoagulation. These concepts are linked together to provide an effective contaminant separation process, which is indiscriminatory as to the contaminant. This is a feature that was not possible in the prior art; the existing art, in most cases, proposes methods which are sensitive to the materials present in the system to be treated. Conveniently, by providing pressure control to the material inlet of the reservoir relative to the outlet, the maximum amount of gaseous oxidant can be retained in solution, thereby providing the smallest possible bubbles in the highest possible density with the greatest possible duration in solution. These features together with the principles of electrocoagulation contribute to the success of the protocol set forth herein.
In order to augment the mass transfer process set forth herein above, it has been found that the combination of that technology together with electrocoagulation produces super results and significantly reduces the limitations and problems associated with the art. In effect, as a further object of one embodiment of the present invention, the control provided with the gaseous oxidant system could be unified with the benefits of electrocoagulation. Accordingly, there is provided a closed system for separating contaminants from an aqueous solution containing contaminants, comprising: an oxidizing stage for oxidizing contaminants in an aqueous solution including:
a closed container containing oxidant and having an inlet in fluid communication with a source of aqueous solution containing the contaminants and an outlet for discharging oxidant and oxidized contaminant; and
an electrocoagulation stage for electrocoagulating oxidized contaminants from the oxidizing stage, the electrocoagulation stage including:
a closed reactor for electrocoagulating oxidized contaminants, the reactor having an inlet in fluid communication with the outlet of the closed container and an outlet for discharging effluent, the reactor configured to diverge from the inlet to the outlet thereof;
electrodes in electrical communication with the reactor, the electrodes being in spaced relation and connectable to a source of power for supplying current to the electrodes;
a power supply for supplying currents to the electrodes; and
a plurality of discrete fluidizable metal reaction surfaces freely fluidizable within the reactor for electrochemically oxidizing the contaminants in the aqueous solution in the presence of the electrodes to isolate the contaminants.
A yet further object of one embodiment of the present invention is to provide a method of separating contaminants from an aqueous solution containing the contaminants, comprising the steps of:
a) providing an aqueous solution containing the contaminants;
b) oxidizing, in an oxidizing phase, contaminants present in the aqueous solution;
c) electrocoagulating, in an electrocoagulation phase, oxidized contaminants from step b), the electrocoagulation phase including:
providing a reactor having an inlet and an outlet from the reactor diverging in configuration from the inlet to the outlet, the reactor including electrode means actuable by a power supply;
providing discrete fluidizable metal reaction surfaces within the reactor;
introducing oxidized contaminants and aqueous solution into the inlet of the reactor;
fluidizing the metal reaction surfaces in the reactor in the presence of electric current;
electrocoagulating contaminants; and
d) separating electrocoagulated contaminants from the aqueous solution.
Of particular value is the fact that the aqueous solution may contain both organic, inorganic waste material or a combination of both.
Having thus described the invention, reference will now be made to the accompanying drawings illustrating preferred embodiments.